This invention pertains to a sensor for the capacitive measurement of the level of material in a container where the material may be at a very high temperature. This is effected by means of a special sensor introduced via an opening in the container's wall, the sensor being pressure tight and electrically insulated.
The capacitive measurement is based, as is known, on the capacity between the sensor electrode and an opposing electrode which is usually formed by the metallic container wall which capacity is variable in respect to the level of material. Capacitive sensors can be used for continuous level measurements or to determine limiting conditions. In every case special demands are made of the sensors when the contents to be measured are in a heated condition. Examples of such contents are hot minerals and flue dust. Hot minerals are ground rock which is heated in rotary rod ovens to temperatures of up to 400.degree. C. and are used in the manufacture of road tops. Hot flue dust is obtained, for example, in coal powered electric power stations and attains the same temperatures. The sensors that are used to measure hot material such as these must be resistant to heat, pressure and abrasion. Beyond that, exists the problem of false measurement caused by moisture which collects at places where the probes are led into the container.
Despite the hot temperature that obtains inside the container, it is possible for condensate to form along the relatively cool container walls. This causes moisture to collect at the place where the sensor passes through the container wall and produces a false reading.